Technical Uno Mia, heater not working :(

[Stevh0]

Ive taken the center console apart to see if I can find any trouble but nothing.

Ive checked the fuses and still nothing.

Any idea why the heater is not working (blows cold air perfectly fine)

 

[alexGS]

Three ideas:

- Thermostat stuck open, engine not warming up. Is there a temperature gauge and is it reading 1/3rd-1/2?

- Heater valve (plastic) on heater radiator seized or operating arm broken.

- Heater radiator clogged (often as a result of the valve seized in the nearly-closed position). On the FIRE engine there is a bypass pipe between the two hoses (in the engine bay) that allows coolant to bypass the heater - necessary when the valve is closed. But as soon as there is any restriction in the heater, the coolant takes the easier path and the heater gets no flow at all.

My suggestion...

Drain the cooling system (4+ litres) from the radiator bottom hose, then put a plastic bowl in the footwell and undo the hoses from the heater radiator (expect some coolant to drain out, less than 1 litre. If this coolant is much rustier than from the main radiator, you know you have a stuck valve or blockage in the heater).

Undo the valve from the heater radiator (two 10mm nuts). Check, clean, replace. There are two types - a sliding-shutter or a rotating-disc. The disc design is more reliable but the sliding design seems to work better in varying the flow.

After you replace the heater valve and reconnect the hoses to the heater, disconnect the hoses in the engine bay and use a garden hose (with good pressure) to back-flush the heater until clean water comes out. Then, connect and refill, including the correct 'antifreeze' (which for you in SA is a corrosion inhibitor and must still be remembered).

-Alex

 

[Stevh0]

Three ideas:

- Thermostat stuck open, engine not warming up. Is there a temperature gauge and is it reading 1/3rd-1/2?

- Heater valve (plastic) on heater radiator seized or operating arm broken.

- Heater radiator clogged (often as a result of the valve seized in the nearly-closed position). On the FIRE engine there is a bypass pipe between the two hoses (in the engine bay) that allows coolant to bypass the heater - necessary when the valve is closed. But as soon as there is any restriction in the heater, the coolant takes the easier path and the heater gets no flow at all.

My suggestion...

Drain the cooling system (4+ litres) from the radiator bottom hose, then put a plastic bowl in the footwell and undo the hoses from the heater radiator (expect some coolant to drain out, less than 1 litre. If this coolant is much rustier than from the main radiator, you know you have a stuck valve or blockage in the heater).

Undo the valve from the heater radiator (two 10mm nuts). Check, clean, replace. There are two types - a sliding-shutter or a rotating-disc. The disc design is more reliable but the sliding design seems to work better in varying the flow.

After you replace the heater valve and reconnect the hoses to the heater, disconnect the hoses in the engine bay and use a garden hose (with good pressure) to back-flush the heater until clean water comes out. Then, connect and refill, including the correct 'antifreeze' (which for you in SA is a corrosion inhibitor and must still be remembered).

-Alex

Great post. The cars temp gauge does not lift much when runing, so its clear we have a problem there.

Ill flush the system over the weekend.

The radiator heater is behind the firewall am I correct? How do I get in there?

 

[Ucof]

..oh the sweet memories

There's nothing I can add that Alex hasnt already said;
Thermostat stuck closed, clogged rad/ cooling system, stuck valve.

 

[Chas Uno]

The cars temp gauge does not lift much when runing, so its clear we have a problem there.

Assuming your temperature gauge and sender are fine then this is probably the root of your problem. I'm suspecting a thermostat that's stuck open, therefore the engine is being overcooled as the engine coolant isn't being allowed to warm up sufficiently before being fed back into the radiator.

You can also test this theory by running the engine for a while and checking to see if the coolant pipes are warming up. The radiator top hose should become too hot to touch under normal operation indicating that the thermostat is keeping the coolant in the engine until it reaches the correct temperature to be fed into the radiator. If it is NOT hot after running the engine then the thermostat is most probably stuck open.

You can also check the coolant pipes heating the heater matrix (two smaller pipes going into the bulkhead/ firewall at the back of the engine). Again, if these are not hot after the engine has been running then this indicates that the engine coolant is being over cooled. I wouldn't suspect any blockages simply because the rest of the coolant circuit is also appearing to run cool as well. If they ARE hot and there's still not much heat coming from the heater then the problem lies with the heater control valve/ flaps. However, if the temperature gauge registers a cool engine then as mentioned above it's almost certainly a thermostat stuck open causing the problems.

First thing you should do is replace the thermostat. They aren't expensive and they are quite easy to change, plus this should hopefully cure your problem. Also, please take care when checking coolant pipes with the engine running as they can get very hot and cause burning, plus make sure no loose hair/ clothing gets in the engine bay near moving parts. I'm sure most people don't need these warnings but there's some that do hence the safety aspect being highlighted and the disclaimer that you follow any advice at your own risk. If in doubt about your abilities get a professional mechanic to deal with it!

 

[alexGS]

The radiator heater is behind the firewall am I correct? How do I get in there?

Chas is right, the thermostat deserves attention first.

You reach the heater from the driver's footwell. You need to remove the footrest/plastic cover under the steering column, if one is fitted (maybe not on your Mia, but it is fitted to some other Mk2 models). Then the heater radiator sits vertically behind the centre console. You should be able to see a rectangular plastic cover (two screws) but you can leave that in place and just undo the water valve, which has one of the hoses attached to it.

It's worth taking the valve off just to look through it and check that it's actually working, as often the lever moves but the valve is stuck closed. Perhaps it's actually working fine and you've wasted half an hour at the most in draining the system and taking the valve off... but better to know that than wonder if it is faulty Or you could just fix the thermostat and see how the heater works after that. How cold does it get in Cape Town, anyway?

-Alex